Recently, a heat treatment apparatus has been used for processes such as forming a thin film, e.g., a silicon epitaxial layer, a silicon nitride film or the like on a front surface of a semiconductor substrate such as a silicon single crystal wafer (hereinafter, referred as wafer) or the like, performing etching thereto or the like.
The heat treatment apparatus comprises, for example, a translucent heat treatment vessel made from quartz or the like, and a susceptor is provided inside thereof for placing and rotating a wafer. A heating apparatus comprising a halogen lamp or the like is provided around the heat treatment vessel so that a wafer placed on the susceptor can be heated from the outside of the heat treatment vessel. Further, a gas supply opening for supplying reaction gas or the like into the heat treatment vessel and a gas exhaust opening are formed at a side portion of the heat treatment vessel, and the heat treatment apparatus is provided with a gas supply apparatus or the like, thereby enabling to supply various reaction gases or the like from the gas supply opening into the heat treatment vessel with predetermined composition and flow rate.
A preheat ring is provided in the heat treatment vessel to surround the side periphery of the susceptor, for preferably performing heat treatment with an in-plane temperature distribution of a wafer W uniformed (for example, Japanese Patent Application Laid Open No. 78863/1995)). The preheat ring is, for example, as a preheat ring 53 shown in FIG. 5, formed in a ring shape with a predetermined width to surround the outer periphery of the susceptor 52, and is supported by a base 54 provided on the side of the susceptor 52 in the heat treatment vessel. FIG. 5A is a top view, and FIG. 5B is a sectional view taken along the line B-B′ of FIG. 5A. The preheat ring 53 is placed on a pocket 54a of the base 54.
The preheat ring 53 is heated together with the wafer W placed on the susceptor 52 by the heating apparatus in heat treatment. For example, in a cold wall type heat treatment apparatus, the heat treatment vessel is cooled by a cooling section for preventing polysilicon or the like from depositing on the inside of the heat treatment apparatus during heat treatment, however, because the preheat ring 53 surrounds the periphery of the susceptor 52, it can be prevented that the temperature at a portion around the wafer W placed on the susceptor 52 is decreased by the effect of the cooled heat treatment vessel. Also, since gas supplied from the gas supply opening into the heat treatment vessel passes over the preheat ring 53 to reach wafer W, the gas is appropriately heated, enabling to preferably perform heat treatment.
Preferably, the preheat ring 53 is, for the purpose thereof, provided as close to the susceptor 52 as possible, while it is required not to contact with the susceptor 52 because the susceptor 52 rotates inside the heat treatment vessel in heat treatment. Therefore, there is a slight clearance A provided between the susceptor 52 and the preheat ring 53.
For preventing the preheat ring 53 from moving on the base 54 by thermal expansion to thereby contact with the susceptor 52, there is a slight clearance C provided between an inner periphery 54aa of the pocket 54 and the preheat ring 53, and the width of the clearance C is set to be within a predetermined range in view of the movement of the preheat ring 53 by thermal expansion.
However, although the heat treatment apparatus is designed such that the susceptor 52 and the preheat ring 53 are concentric with each other as shown in FIGS. 5A and 5B, a center 52b of the susceptor 52 may be slightly misaligned relative to a center 53a of the preheat ring 53 as shown in FIG. 6 due to error in accuracy of each member forming the heat treatment apparatus and assembling accuracy. Specially, in a case of a heat treatment apparatus for processing a wafer with large diameter, a misalignment of about 1 to 2 mm would occur, thereby the susceptor 52 may contact with the preheat ring 53.
Occurrence of such the contact would generate a large amount of particles because the susceptor 52 and the preheat ring 53 rub each other during heat treatment, which adhere to the wafer to cause crystal defect, resulting in lowering of yield.
Although the preheat ring 53 is moved in the pocket 54a of the base 54 depending upon a misalignment of the susceptor 52 for preventing such the contact, the clearance C between the inner periphery 54aa of the pocket 54a and the preheat ring 53 is limited as described above. When the inner diameter of the preheat ring 53 is enlarged, the distance between the preheat ring 53 and the susceptor 52 becomes large, thereby obstructing to sufficiently fulfill the function, which is disadvantageous.
Accordingly, for avoiding the contact of the susceptor 52 with the preheat ring 53, operations such as adjusting a support section or the like of the susceptor are needed, which are extremely cumbersome and require a lot of time. Specially, after maintenance such as cleaning of the heat treatment vessel or the like, it would take a considerable amount of time for adjusting the susceptor 52 and the preheat ring 53, which is causative of long non-operating time.
An object of this invention is to provide a heat treatment apparatus and a heat treatment method, in which a contact of a susceptor with a preheat ring can be easily prevented, and generation of particles can be reduced to preferably perform heat treatment.